In this project the incidence, distriubution and ecology of tick-borne disease agents, arboviruses and rickettsiae, are studied. These pathogens are isolated in tissue cultures or animals from field-collected materials and are serologically identified. Viruses, if new, are physicochemically and biologically characterized and taxonomically classified. Of particular importance is the delineation of vector-relationships and human disease potential of the increasing number of tick-borne viruses in the United States.